This invention relates generally to memories or storage for electronic devices.
A wide variety of memory is available for a variety of specialized applications. For example, volatile memories, such as dynamic random access memory (DRAM) and static random access memory (SRAM), may be utilized for fast access to data. However, DRAM memory is difficult to integrate and SRAM memory is relatively high in cost.
Another type of memory is flash memory. However, flash memory is slower in write mode and has a limited number of write and erase cycles. Because it is nonvolatile memory, flash memory may be applicable to both code and data storage applications.
In a wide variety of electronic devices, there is a need for relatively low cost memory that performs a variety of different functions. Examples of such devices include portable devices, such as cellular telephones, personal digital assistants (PDAs), notebook computers, wearable computers, in-car computing devices, web tablets, pagers, digital imaging devices, and wireless communication devices, to mention a few examples.
Currently, the storage on processor-based systems is largely handled by semiconductor memories, such as SPAMs and DRAMs, and by mechanical devices, such as optical and magnetic disk drives. Disk drives are relatively inexpensive but have relatively slower read and write access times. Semiconductor memories are more expensive, but have relatively fast access times. Thus, electronic devices using a combination of disk drive and semiconductor memories for storage may place the bulk of the data and code in the disk drive and store frequently used or cache data on semiconductor memories.
However, none of the existing technologies adequately provide the needed attributes for a truly portable device including lower cost, lower power consumption, non-volatile memory compactness and easy integration. Thus, there is a need for new types of memory.
One new memory type is the polymer memory. The polymer memory involves polymer chains with dipole moments. Data may be stored by changing the polarization of a polymer between conductive lines. For example, a polymeric film may be coated with a large number of conductive lines. A memory location at a cross-point of two lines is selected when the two transverse lines are both charged. Because of this characteristic, polymer memories are one type of cross-point memory. Another cross-point memory being developed by Nantero, Inc. (Woburn, Mass.) uses crossed carbon nanotubules.
Cross-point memories are advantageous since no transistors are need to store each bit of data and the polymer layers can be stacked to a large number of layers, increasing the memory capacity. In addition, the polymer memories are non-volatile and have relatively fast read and write speeds. They also have relatively low costs per bit and lower power consumption. Thus, the polymer memory has a combination of low cost and high capacity that fits well in handheld data storage applications.
Phase-change materials may also be utilized to create memories. In phase-change memories, a phase-change material may be exposed to temperature to change the phase of the phase-change material. Each phase is characterized by a detectable electrical resistivity. To determine the phase of the memory during a read cycle, current may be passed through the phase-change material to detect its resistivity.
The phase-change memories are non-volatile and high density. They use relatively low power and are easy to integrate with logic. The phase-change memory may be suitable for many code and data storage applications. However, some high-speed volatile memory may still be needed for cache and other frequent write operations.
Thus, there is still a need for a memory solution for low cost, portable applications.